The purpose of these studies is to establish a better understanding of the energy metabolism in tissues in vivo. Towards this goal, the laboratory concentrates on the use of non-invasive and non-destructive optical and NMR techniques to evaluate the biochemical and physiological function of the heart with regard to energy metabolism. Of special interest to the laboratory is the control of oxidative phosphorylation and blood flow in the intact heart. The following major findings were made over the last year: 1) Our model of oxidative phosphorylation has developed into a equivalent circuit model which has permitted several specific predictions with regard to the role of substrate oxidation, F1- ATPase activity and the free energy available for work. To solve this model, new measures of the effect of carbon driving force on oxidative phosphorylation have been performed using simultaneous on-line measures of oxygen consumption rate(clark electrode), NADH/NAD(fluorescence), and mitochondrial membrane potential (TPP+ sensitive electrodes). These studies demonstrate that forward activity of the F1-ATPase is regulated by the available energy from a given carbon substrate. This type of impedance matching assures an efficient transfer of power from intermediary metabolism to the mitochondrial membrane potential. The mechanism for this metabolic impedance matching is still under investigation with several candidates including mitochondrial volume and free calcium concentrations. 2) Direct NADH fluorescence measures and optical spectroscopy studies in the intact porcine heart reveal that the NADH redox state is not affected by increases in metabolic rate. These data support the notion that the cytosolic ADP and Pi concentrations are not changing with increases in workload, but the system is regulated via an independent mechanism. Previous data suggests that a direct modification of F1-ATPase activity is the site of modification. 3) Similar studies evaluating the effect of work on tissue oxygenation levels in the heart reveal that increases in net myocardial oxygenation occur with increases in work, in vivo. These data demonstrate that tissue hypoxia is not the signal for increased blood flow during exercise induced hyperemia. They also suggest that the control network for coronary blood flow control results in a net increase in tissue oxygen tension with increases in work through an undefined mechanism.